Trailers are commonly used to transport goods over long distances. The term “trailer” is used in this specification to mean any size or shape of container intended to be towed by a vehicle. The clearance required between the ground and the underside of the trailer chassis means the deck of the trailer is significantly elevated, making it difficult to load and unload the trailer with large and/or heavy items.
It is therefore common for trailers to have a pivot point about which the deck may be rotated to some degree, tilting the deck downwards towards the rear end to facilitate easier loading and unloading, while the trailer chassis may remain level and attached to the vehicle for stability. This solution is not ideal however, as the inclined deck of the trailer is not suitable for loading and/or unloading many items.
An improved solution to this problem would be to provide a mechanism whereby the deck of the trailer may be lowered relative to the wheels and parallel with the ground. Ideally, the mechanism should allow the underside of the chassis to be lowered to the extent that it rests on the ground, such that the trailer deck is substantially even with the ground. This would provide a very stable platform for loading, and items may be simply pushed or wheeled onto the deck with a hand trolley, wheelbarrow, dolly, or similar.
The main difficulty in designing such a mechanism is that the drawbar should remain attached to the tow-bar of the towing vehicle for stability while being lowered and elevated, and the wheels, axles, and suspension assemblies etc. of the trailer must be retracted above the underside of the chassis, while maintaining sufficient structural strength for the trailer to bear heavy loads.
The applicant is not aware of any trailers capable of sufficiently lowering the deck parallel with the ground to ground level while attached to an unmodified standard tow-bar on the towing vehicle.
U.S. Pat. No. 6,592,139 to Shanahan, for example, discloses an elevatable trailer having a telescopic frame or chassis, whereby retraction and extension of the frame causes wheel-mounting member to pivot such that wheels are raised and lowered, respectively, with respect to the frame. The drawbar is fixed relative to at least a portion of the frame, and is therefore lowered and raised with the frame. To maintain the trailer parallel with the ground, a modified tow-bar is required on the towing vehicle as shown in detail in FIG. 12 of Shanahan. Due to the design, the modified tow-bar offers little stability to support the trailer as it is lowered. Parallel lowering of the trailer is not possible when coupled with an unmodified tow-bar.
Australian Patent Application No. 2005200640 entitled ‘Trailer’ discloses a trailer having a drawbar pivotally attached to a support frame or chassis, and hydraulic cylinders acting between the draw bar assembly and each wheel support member. Retraction of the hydraulic cylinders causes both the wheel support members and the drawbar to pivot, lowering the chassis towards the ground. This solution is not ideal, however.
It is therefore an object of the invention to provide a trailer with a deck which can be easily lowered and elevated while attached to a towing vehicle and overcoming or ameliorating at least one disadvantage of the prior art, or at least to provide the public with a useful choice.